The nucleated cells seen in normal adult CSF are predominantly lymphocytes and monocyte/macrophages. A rare neutrophil may be seen. An increased number of lymphocytes, monocytes, or neutrophils in CSF is termed pleocytosis. Morphologically normal cells can be seen in abnormal numbers in meningitis and inflammation.

The monocyte/macrophage appears when clean up of the CSF is necessary because of degenerating cells and debris, often due to a subarachnoid hemorrhage (SAH) or meningitis.

Cells that may be seen in cerebrospinal fluid may be divided into four categories:

Mature peripheral blood cells

Immature hematopoietic cells

Tissue cells

Malignant cells

Tissue cells are often seen in spinal fluid samples. It is important to recognize these cells so that they are differentiated from tumor and blast cells. Pathologists must review any slides that have presumptive malignant cells, unidentified cells, or immature stages of cells, such as blasts. Since criteria for review may vary from one laboratory to another, be sure to check the requirements in your laboratory before reporting the differential.